Biology 3i - Life Processes

Biology 3(i)

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  • Created by: Lauren
  • Created on: 08-05-11 15:58

Gas and Solute Exchange

Gases and other dissolved substances move by DIFFUSION, OSMOSIS and ACTIVETRANSPORT

Diffusion is the passive movement of particles from an area of high concentration to an area of low concentration

Osmosis is the movement of water molecules across a partially permeable membrane from a region of high water concentration to a region of low water concentration.

These substances have to move through an exchange surface, which have to allow enough of the necessary substances to pass through.Exchange surfaces are adapted to maximise effectiveness.

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Structure of Leaves

The underneath of the leaf is an exchange surface covered in stomata. The size of the stomata is controlled by guard cells which close the stomata if the plant is losing water faster than it is being replace by the roots - without these the plant would wilt. The flattened shape of the leaf increases the area of the exchange surface which makes it more effective.

The walls of the cells inside the leaf form another exchange surface. The air spaces in the leaf increases the area of this surface meaning there's more chance for carbon dioxide to reach the cells.

Carbon dioxide diffuses in through the stomata, then diffuses into cells where photsynthesis happens. Water vapour and oxygen diffuse out through the stomata (water vapour is actually lost from all over the leaf surface, but mostly through the stomata)

The water vapour escapes by diffusion. This diffusion is called TRANSPIRATION which works quickest in HOT DRY WINDY conditions.

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The Breathing System

The lungs are in the thorax which is seperated from the lower part of the body by the diaphragm .

The air you breathe in goes through the trachea (windpipe). This splits into two tubes called bronchi (each one is a bronchus) one going to each lung. The bronchi split into progressively smaller tubes called bronchioles, which finally end at the alveoli where the gas exchange takes place.

Breathe in... Intercostal muscles and diaphragm contract (diaphragm flattens). Thorax volume isncreases which decreases the pressure drawing air in.

Breathe out... Intercostal muscles and diaphragm relax (diaphragm moves up) Thorax volume decreases which increases the pressure forcing air out.

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Diffusion through Cell membranes

Lungs job: To get oxygen from the air into your bloodstream to get into cells for respiration + to remove carbon dioxide from the blood.

Alveoli is where the gas exchange takes place. They are specialised to maximise diffusion of oxygen and carbon dioxide. For this they have:

1) An enormous surface area     2) A moist lining for dissolving gases                   3) very thin walls      4) a copious blood supply


The inside of the small intestine is covered in millions of villi. They help get digested food absorbed into the bloodstream. For thsi they have:

1)  an enormous surface area             2) a single layer of surface cells                  3) a very good blood supply to assist quick absorption

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Active Transport


Absorption AGAINST a concentration gradient, needs energy from respiration to make it work. 2 EXAMPLES.

Root Hair Cells: The cells on the surface of plant roots grow into long hairs which stick out in the ground giving the plant a big surface area for absorbing water and mineral ions. But the concentration of minerals in higher in the root hair cell than in the soil so ACTIVE TRANSPORT IS USED.

The Gut: ( we want nutrients in the blood). When there's a higher concentration of glucose and amino acids in the gut they diffuse naturally into the blood. But sometimes it's the other way round, so active transport is used, when there is more in the blood than in the gut.

remember! active transport uses energy - remember sheep in a field.

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The Circulation System

Job of Circulation System: DELIVERY SERVICE- deliver food and oxygen to every cell in the body. WASTE COLLECTION SERVICE-carries waste products like carbon dioxide and urea to where it can be removed from the body.

Humans have a DOUBLE CIRCULATION SYSTEM. The heart is two pumps. The right side pumps deoxygenated blood to the lungs to collect oxygen and remove carbon dioxide. The left side pumps this oxygenated blood around the body.

Arteries carry blood away from the heart at high pressure. Arteries carry oxygenated blood and veins carry deoxygenated blood. (exceptions: pulmonary artery and pulmonary vein)

The arteries eventually split off into thousands of tiny CAPILLARIES which take blood to EVERY cell in the body.

The veins then collect the "used" blood and carry it back to the heart at LOW PRESSURE to be pumped round again.

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CAPILLARIES use diffusion to deliver food and oxygen direct to body tissues and take carbon dioxide and other waste materials away. Their walls (endothelium) is just ONE cell thick to make diffusion easier. They can only be seen with a microscope.

Blood consists of FOUR main parts.

1) White blood cells 2) Red blood cells 3) Plasma 4) Platelets-(small fragments of cells that help blood to clot at a wound)

Red Blood Cells

Job:carry oxygen from the lungs to all the cells in the body. They have a CONCAVE DOUGHNUT shape helps them pass smoothly through capillaries to reach body cells and gives them a large surface area for absorbing oxygen. They contain a pigment called haemoglobin which absorbs oxygen - no nucleus so more room for it.

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Plasma is a pale straw coloured liquid that carries everything in Blood. It carries:

Red blood cells, white blood cells, platelets

Nutrients like glucose and amino acid (these are soluble products of digestion which are absorbed from the gut and taken to the cells of the body)

Carbon dioxide from the organs to the lungs

Urea from the liver to the kidneys


Antibodies and antitoxins produced by the white blood cells.

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Muscles are made of muscle cells. These use oxygen to release energy from glucose (RESPIRATION) which is used to contract the muscles.

An increase in muscle activity requires MORE glucose and oxygen to be supplied to the muscle cells - for this to happen, blood has to flow at a faster rate. This is why exercise: increases heart rate, dilates the arteries which supply blood to the muscles and increases your breathing rate, making you breather more deeply to meet demand for extra oxygen.

Some glucose from food is stored as GLYCOGEN. Glycogen is mainly stored in the liver, but each muscle also has its own store.

During vigorous exercise, muscles use up glucose rapidly and have to draw on their gycogen stores to provide more energy. But eventually, the glycogen stores get used up.When the glycogen stores run low, the muscles don't get the energy they need to keep contracting, and they get TIRED.

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During vigorous exercise when your body can't supply enough oxygen to your muscles, they start doing anaerobic respiration. anerobic = without oxygen. It's the complete breakdown of glucose which produces lactic acid.

GLUCOSE -> ENERGY + LACTIC ACID Not best way to convert glucose into energy because lactic acid builds up in the muscles which is painful and makes muscles get tired. It also doesn't release as much energy as aerobic respiration. But you can keep using your muscles for a while longer.

Anaerobic respiration leads to an oxygen debt after exercise - like repaying the oxygen that you didn't get to your muscles in time. So you have to keep breathing hard for a while after you stop to get oxygen into your muscles to oxidise the painful lactic acid to harmless carbon dioxide and water. While high levels of co2 and lactic acid are detected in the blood (by the brain) pulse and breathing rate stay high to rectify the situation.

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